Lasers are increasingly used in different applications ranging from metal cutting to skin treatment and cosmetic procedure. Often in these applications, the laser beam must be manipulated spatially in order to move the beam over the area to be treated. In the case of metal cutting, the beam may need to be move over the metal to achieve a desired cutting path over the contours of the work piece. In the case of skin treatments, the beam may need to be moved in order to follow the contour of a body part to cover an area of the body with the beam. The beam delivery system often used in these applications consists of multiple mirrors which can rotate and move. An example of such a beam delivery system is an articulated arm system. In such a system, as beam is manipulated, the mirrors rotate and move. A consequence of the movement of the mirrors in such a system is that the delivered beam is rotated around its axis, and the amount of rotation depends on the position and orientation of the mirrors. A plane polarized beam going through such a system will emerge with its polarization plane rotated by a varying amount depending of the position and orientation of the mirrors, so that as the beam is manipulated the plane of polarization of the output beam will rotate continuously.
In some instances it is beneficial to maintain the polarization plane fixed. In the case of metal cutting, it is well known that the speed of cutting that can be achieved with a given amount of beam power is dependent on the polarization of the beam relative to the direction of the beam travel over the work piece. In the case of skin treatments, it is often advantageous to be able to convert the wavelength of the beam for treating different dermatologic conditions. Wavelength conversion can be accomplished by using the beam to pump another laser medium to generate a second laser beam, or by nonlinear frequency conversion techniques. In both of these, the conversion process often require that the polarization of the beam be fixed with respect to an optical axis of the laser medium to be pumped or an optical axis of the non-linear medium used. In this case, if the wavelength conversion is more conveniently done after the beam is put through an articulated arm, then the uncontrolled rotation of the polarization of the beam as the arm is manipulated will preclude such a system.
This present apparatus is intended to support a plane polarized beam to be propagated through a beam manipulation system consisting of multiple moveable mirrors while maintaining its plane of polarization constant.